Varifocal optical system for zoom lens having ultra-high zoom ratio

ABSTRACT

Varifocal optical system for zoom lens of this invention attains a zoom ratio larger than 20 and consists of convergent, divergent and convergent lens groups. The second group is movable over a wide range and the third group is moved in the direction opposite to that of the second group so as to constitute the zoom operation maintaining the position of image surface constant.

I United State 6 l 13,609,005

[72] Inventor sollichi Nakamun [56] References Cited 1 A l N $33 UNITEDSTATES PATENTS [2 1 P 3,045,546 7/1962 Cook 350/l86 [22] PM 1969 3 507555 4/1970 lSShiki 350/184 [45] Patented Sept. 28, 1971 [73] AssigneeNippon Kogaku KJC. FOREIGN PATENTS Tokyo, Japan 1,095,539 12/1967 GreatBritain 350/l84 Pnomy 2:53 1968 Primary Examiner-John K. Corbin I 3 l 143/728 Attorney-Ward, McElhannon, Brooks & Fltzpatrlck [54] VARIFOCALOPTICAL SYSTEM FOR ZOOM LENS g g f 't g i g RATIO ABSTRACT: Varifocaloptical system for zoom lens of this inm a vention attains a zoom ratiolarger than 20 and consists of con- [52] US. Cl 350/184, vergent,divergent and convergent lens groups. The second 350/214 group ismovable over a wide range and the third group is [51 Int. Cl G02b 15/ 14moved in the direction opposite to that of the second group so [50]Field 0! Search 350/ I84, as to constitute the zoom operationmaintaining the position 186 of image surface constant.

FIRST LENS 8593111952015 T1150 1.511s RELAY LENS I RIB R19 20 21 22 1s14 PATENTED serza I97I 3,609,005

SHEET 2 or 4 CHROMATIC ABERRATION DISTORTION PATENTEU SEP28 I97! sum 3or 4 FIRST LENS 3 SECOND LENS THIRD LENS RELAY LENS FIG. 4A

RI 2 5 R4 R536 m8 SAG|TAL ASTIGMAT --MERIDIONAL PATENTEU SEP28 I97!SHEET 0F 4 g-Line DISTORTION VARIFOCAL OPTICAL SYSTEM FOR ZOOM LENSHAVING ULTRA-HIGH ZOOM RATIO The present invention relates to avarifocal optical system for zoom lens having a zoom ratio larger thanand of the type in which the varifocal optical system comprises of threeconvergent, divergent and convergent lens groups so that the second lensgroup is moved over a wide range for zooming while the third lens groupis moved in the direction opposite to that of the second lens group,thereby maintaining the position of the image surface constant over thewhole field. (The tenn variable focal optical system" is used in thisspecificationto designate the optical system consisting of a lens groupmainly for focusing, a group mainly for varying the focal length and alens group mainly for maintaining constant the image surface of the zoomlens so as to be distinguished from the relay lens system following thevarifocal optical system).

In case of a zoom lens having a high zoom ratio the following problemsarise;

l. The chromatic aberration at the longer focal length must becorrected;

2. The high-order spherical aberrations over the range from the focallength in the vicinity of (minimum focal length X zoom ratio) to thelonger focal length must be balanced while the chromatic or colorvariation caused by this balancing must be corrected;

3. The coma at the longer focal length must be corrected by suitablybalancing the fulfillment of the sine conditions; and

4. The aberrations due to the movement over a long range of the firstlens group (focusing lens group) for photographing a short-distanceobject must be stabilized.

In view of the above, the present invention has for its primary objectto provide a varifocal optical system for a zoom lens system having anultra-high-zoom ratio and excellent performance and being capable ofeliminating substantially all the problems encountered in theconventional zoom lens system without varying the aperture over thewhole zooming range.

The present invention will be described more in detail referring to theillustrative examples shown in the attached drawing, in which:

FIG. 1 shows a cross section of a first example of an 8 mm. cinephotographic lens (for super 8) embodying the optical system of thisinvention;

FIGS. 2 A, B, C and D show respective aberrations of the system of thefirst example at the shortest, intermediate 1, intermediate 2 and thelongest focal lengths respectively;

FIG. 3 shows a cross section of a second example of photographic lensfor an industrial television camera embodying the optical system of thepresent invention; and

FIGS. 4 A, B, C and D show respective aberrations of the second exampleat the shortest, intermediate 1, intermediate 2 and the longest focallengths, respectively.

The varifocal optical system of the present invention comprises a firstconvergent lens group a second divergent lens group and a thirdconvergent lens group, said second lens group being moved over arelatively wide range thereby accomplishing zooming while said thirdlens group is moved in the direction opposite to that of the second lensgroup, thereby maintaining constant the image surface.

Furthermore, according to the present invention the followwhere R and R,=radii or curvature of front and rear free surfaces of the cemented lensof the first component of the first lens group; R, and R qadii ofcurvature of front and rear surfaces of the first lens component of thesecond lens group: f, =the compound focal length of the second lensgroup; f, =the compound focal length of the second lens group except thelast cemented lens; f =the focal length of the first component of thesecond group f, =the component focal length of the third lens group; R=the radius of curvature of the cemented interface of the last cementedlens of the third lens group, and nf and nr q'ndexes of the convex andconcave lenses which compose the last cemented lens of the third lensgroup.

Next the significance of the above-described conditions will bedescribed in more detail.

When the value of the condition (R, +R,)(R -R,) is larger than zero, notonly the curvature of the image surface but also other aberration may bebalanced at the infinity distance position at both of the minimum andmaximum focal lengths, how ever, when an object is located at arelatively shorter distance, i.e., 5 to 10 times the maximum focallength of the zoom lens, the curvature of the focal plane sphericalaberrations and other aberrations on the longer focal length side areunbalanced so that the performance of the zoom lens is deteriorated. 0nthe other hand, when the value is less than 1.5, it is diflrcult tobalance the aberrations with each other at the infinity distanceposition. Especially the convergent bending toward the object becomeslarger so the selection of types of glasses for balancing the achromaticfeature of the whole first lens group will become impossible. Thus, itis impossible to manufacture such first lens group.

The conditions (II) and (III) are for minimizing the color variation ofthe spherical aberration due to the variations of high-order sphericalaberrations and the increased coma caused by the unbalance of the sineconditions from the intermediate to the maximum focal lengths, which arevery difiicult to be solved satisfactorily in case of the zoom lenshaving an ultra-high zoom'ratio.

When the ratio of the condition (III) is in excess of the upper limit,the spherical aberration of the helium d line is overcorrected so thatthe color or chromatic variation of the spherical aberrations by thelight rays whose wavelengths are shorter than the helium d line will bemuch increased. On the other hand, when the ratio is less than the lowerlimit, the color or chromatic variation of the spherical aberrations dueto the undercorrected, spherical aberrations at the maximum focal lengthwill be increased.

The condition (II) will be investigated under the assumption that thecondition (III) is satisfied. When the ratio (R, +R R is larger than 5,the sine condition will become too much negative on the maximum focallength side so that the coma will be increased. On the other hand, whenthe ratio is which satisfies the conditions (II) and (III) is forobtaining suitable combinations of the types of the glasses for carryingout the suitable correction of chromatic aberrations imposed upon thesecond lens group as a whole, thereby attaining a suitable balance ofaberrations.

The condition (b) of (IV) must be satisfied in order to improve thecolor of chromatic variation of the spherical aberration due to thevariations of the high-order spherical aberrations from the intermediatefocal length to the longer focal length. When both of the conditions (a)and (b) of (IV) are satisfied, various aberrations may be suitablybalanced and especially the coma are satisfactorily corrected all overthe magnification range. That is, when the value of R/f, is less than0.7, the coma at the intermediate focal length will be increased so thatthe aberrations may not be well-balanced all over the magnificationrange. On the other hand, when the value is in excess of 1.0, thespherical aberration at the max- After the verifocal optical systemsatisfying the abovedescribed conditions is obtained, the Petzval sum ofthe relay lens system following the varifocal optical system may besuitably corrected in consideration of the ratio of the range of thevariation of the focal length of the varifocal optical system to thecompound focal length of the total zoom lens system, whereby the highperformance zoom lens may be provided in a relatively simple manner.

Next some examples of the present invention will be described.

FIG. 1 is a diagrammatic sectional view of 8 mm. cine photographic zoomlens to which is applied the present invention. When the aperture ratiois F:l.8 and the focal length,

[=60 to 128.5, the design data of the lens system are as folwhere R-radius of curvature d thickness of center of lens element and spacingbetween two adjacent lenses.

n =indcx of refraction of used glass at d line, and

v, =Abbe number of glass used.

In this example, the relay lens group had a simple constructionconsisting of a simple divergent lens, a simple convex lens and adoublet. However, when required, the simple convergent lens and thedoublet may be replaced with any other complex optical system such as atriplet. The two prisms interposed in this optical system are fordirecting the light rays to a finder and for measuring the luminousintensity of the subject and constitute no essential part of the presentinvention.

FIG. 2 shows the aberration curves of the first example at the minimumfocal length, f =6.0; the first intermediate focal length, f =22.2; thesecond intermediate focal length, f=49.5; and the maximum focal lengthof,f=l 28.5. It will be seen that the aberrations are well correctedover the whole zooming range. FIG. 3 shows the second embodiment of thepresent invention applied to the industrial television camera zoom lens,The aperture ratio was F 3.5; and the focal length, f =1 3.5 to 285.5.The design date are as follows:

' where R adius of curvature d =thickness of center of lens and spacingbetween two adjacent lenses,

n.=index of refraction of glass used on d line vd =Abbe number of glassused.

In this example, the relay lens group consists of a divergent lens groupand a convergent lens group, and the focal length of each group of thevarifocal optical system was made shorter in order to provide the zoomlens compact in size. Therefore, in order to prevent the Petzval sum ofthe total system from becoming negative, the indexes of refraction ofthe divergent elements of the convergent lens group of the relay lensgroup are increased while those of the convex elements decreased, sothat the overall balance was attained.

FIG. 4 shows the aberration curves of the second example at the minimumfocal length, f =l'3.5; the first intermediate focal length, f =49.4;the second intermediate focal length, f =l 10.0; and the maximum focallength, f=285.5. lt will be seen that the aberration are well correctedover the whole zooming range.

From the foregoing, it will be clear that various zoom lens systemshaving ultra-high zoom ratios and being well cor-. rected over the wholezooming range may be provided when the above described conditions (I) to(IV) are satisfied so that they may be more advantageously used invarious fields.

What is claimed is:

1. A varifocal optical system for zoom lens systems located in front ofa rear convergent optical system and having an ultra high zoom ratiocomprising;

A first convergent stational lens group consisting of a first positivemeniscus doublet of which the front and rear surfaces and the cementedsurfaces are convex toward the object, a second biconvex doubletprovided behind said first doublet, the cemented surfaces of said seconddoublet being concave toward the object, and a third positive meniscussimple component placed behind said second doublet, the surfaces of saidthird component being convex toward the object;

A second divergent moveable lens group consisting of first and secondnegative meniscus simple components of which the surfaces are convextoward the object, and a third biconcave doublet placed behind saidsecond meniscus component, the cemented surfaces of said third doubletbeing convex toward the object; an

A third convergent moveable lens group consisting of a first positivemeniscus component of which the front surface is concave toward theobject, second and third biconvex simple components placed behind saidfirst positive meniscus component, and a fourth biconvex doublet placedbehind said third biconvex component, the cemented surfaces of saidfourth doublet being concave 'toward'the object, whereby said secondlens group is moved over a wide range for affecting zooming operation,while the third lens group is moved in the direction opposite to that ofsaid second lens group for maintaining the position of the image surfaceconstant.

2. An optical system comprising a first lens group, a second lens group,a third lens group and a relay lens group and a relay lens group andsatisfying the following data:

where R denotes radius of curvature, d denotes a central thickness oflens or spacing between adjacent lenses, n denotes a refractive index ond-line of the glass used and v denotes Abbe number of the glass used.

3. An optical system comprising a first lens group, a second lens group,a third lens group and a relay lens group and satisfying the followingdata:

where R denotes radius of curvature, d denotes a central thickness oflens or spacing between adjacent lenses, n denotes a refractive index ond-line of the glass used and v denotes Abbe number of the glass used.

, UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,609,005 Dated September 28, 1971 Inv0ntor(s) Souichi Nakamura It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 3, delete "of";

line 58, after "surface." add The first lens group comprises a firstpositive meniscus doublet of which the front and rear surfaces and thecemented surfaces are convex toward the object, a second bi-convexdoublet provided behind said first doublet, the cemented surfaces ofsaid second doublet being concave toward the object, and a thirdpositive meniscus simple component placed behind said second doublet,the surfaces of said third component-being convex toward the object.

The second lens group comprises first and second negative meniscussimple components of which the surfaces are convex toward the object,and a third bi-concave doublet placed behind said second meniscuscomponent, the cemented surfaces of said third doublet being convextoward the object.

The third lens group comprises a first positive meniscus component ofwhich the front surface is concave toward the object, second and thirdbi-convex simple components placed behind said first positive meniscuscomponent, and a fourth biconvex doublet placed behind said thirdbi-convex component, the cemented surfaces of said fourth doublet beingconcave toward the object line 74, change "or" to of. Column 2, line 14,change (R R (R R to (R R /R R lines 48 and c ange (R R (R to (R RlO/RURN FOJOLU HESS} USCOMNPDC 633764769 UNITED S'IA'IES PA'H CNT OFFICE CERTE FICATE OF CORRECTION Patent -l, 6 Q2 D D 5 Dated September 28 l97l lSouichi Nakamura It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Continued Page 2:

Column 2, line 62, change "of" (first occurrence) to on--. Column 3,line 1, change verifocal" to varifocalline 36 change "(51 =l02.888 2731" to d =lO2. 888 2 .73l;

line 49, change "d 4=2.l48 to 24= 22.135--. Column 4, line 30, change "d=llO.549 2.699" to d =ll9.549 2.699-,- line 44, change "a =3.so1 26.953"to -d =3.60l 26.953-. Column 5, line 28, change "an" to -and. Column 6,line 40, change vd =62.4" to -vd =64.2.

Signed and sealed this 27th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer CommissionerofPatents

1. A varifocal optical system for zoom lens systems located in front ofa rear convergent optical system and having an ultra high zoom ratiocomprising; A first convergent stational lens group consisting of afirst positive meniscus doublet of which the front and rear surfaces andthe cemented surfaces are convex toward the object, a second biconvexdoublet provided behind said first doublet, the cemented surfaces ofsaid second doublet being concave toward the object, and a thirdpositive meniscus simple component placed behind said second doublet,the surfaces of said third component being convex toward the object; Asecond divergent moveable lens group consisting of first and secondnegative meniscus simple components of which the surfaces are convextoward the object, and a third biconcave doublet placed behind saidsecond meniscus component, the cemented surfaces of said third doubletbeing convex toward the object; an A third convergent moveable lensgroup consisting of a first positive meniscus component of which thefront surface is concave toward the object, second and third biconvexsimple components placed behind said first positive meniscus component,and a fourth biconvex doublet placed behind said third biconvexcomponent, the cemented surfaces of said fourth doublet being concavetoward the object, whereby said second lens group is moved over a widerange for affecting zooming operation, while the third lens group ismoved in the direction opposite to that of said second lens group formaintaining the position of the image surface constant.
 2. An opticalsystem comprising a first lens group, a second lens group, a third lensgroup and a relay lens group and a relay lens group and satisfying thefollowing data:
 3. An optical system comprising a first lens group, asecond lens group, a third lens group and a relay lens group andsatisfying the following data: